Around the same time as David Cameron climbed into a glacier, I too went into a hole in Scandanavia

Mr Brown's attitude to Mr Cameron's environmental interests is certainly refrigerated. Gordon Brown generates resentment in the way that Soviet-era factories produced pollution, and those around him find it hard to decide which is his favourite outlet: Tony Blair or David Cameron. Despite the Tories' recent lack of progress in the polls, Gordon Brown is alarmed and outraged by David Cameron's attempts to reposition his party. The Chancellor sees this as a threat to his entitlement: long years of premiership with a secure majority. That is why he is behaving like a troll with a glacial hangover.

Mr Brown may also be uneasily aware that Mr Cameron has an advantage in the environmental debate. The Tory leader's body language is more persuasive. The average voter, unsure whether he knows the difference between CO2 and CFCs will judge the contenders according to subliminal impressions. Here, Mr Cameron wins and deservedly so.

He has always been interested in environmental issues. Like Margaret Thatcher, he is convinced of the dangers of climate change. I recall many an argument on that topic around heated dinner tables. Brought up in the country, Mr Cameron's emotional roots are in the countryside, and this colours his politics.

Although he is a son of the manse, Mr Brown's emotional roots are in the old Scottish Labour movement and in the heavy industries at its core. Not long ago, a majority of Scots lived within 50 miles of a coalmine, a shipyard or a steelworks. Many Scottish socialists believe that they still should. Gordon Brown is more sophisticated than that, but he has something in common at the level of sentiment with those who still instinctively revere the belching smokestacks.

David Cameron's sentiments are aroused by taking his children to admire the pigs in the neighbouring farmyard and chatting to old farm-workers with accents like a wheel of aged cheddar who live only 80 miles from London but the same distance from the 20th century, let alone the 21st. The difference shows.

There is also a divergence in intellectual approach, once again in David Cameron's favour. Gordon Brown makes enormous claims for his climate-change levy, an attempt to assist the environment by fiscal means. But there is no justification for his boasts. The climate change levy is a misnomer and a fraud. A mere tax upon energy consumption by business, it falls on the just and the unjust alike. It makes no distinction between firms which do nothing to avoid damaging emissions and their competitors who try to clean up energy use. The climate change levy is just another stealth tax.

David Cameron would replace it with a carbon tax. The details have still to be worked out, but the principle is clear. This would be a tax to help the environment, not an excuse to add to business costs.

That should be easy for the Tories. But there will be harder issues. It appears that Tony Blair has been persuaded of the merits of nuclear power as the only means of meeting mankind's need for clean energy. It remains to be seen whether the PM will find the courage to act on his convictions - and whether Mr Brown will allow him to do so. David Cameron has still to make up his mind about nuclear power; he has not yet had enough time to review the arguments. But this is the biggest energy conundrum, as well as the most controversial one.

Around the same time as David Cameron climbed into a glacier, I too went into a hole in Scandinavia. I was visiting a nuclear power plant near Helsinki and we looked at an underground nuclear waste disposal facility.

Finnish public opinion has proved amenable to nuclear power, for a reason which the politicians and scientists are reluctant to acknowledge: Russia. Finland's huge neighbour is awash with energy. But Finns value their hard-won independence too dearly to be willing to risk energy blackmail. In Finland last week, there was still snow on the ground and ice on the lakes. Early spring in Finland is as harsh as Britain's bleak mid-winter.

Last week Gazprom, the Russian gas company, reminded Europe how dependent it is on Russian supplies to avoid hypothermia. If Gazprom had been the European nuclear industry's public relations consultant, it could not have done a better job.

The world needs a reliable source of post-carbon energy. There is only one candidate: nuclear power. No country is more environmentally conscious than Finland; the Finns recognise the need for nuclear energy. No country is more cynically committed to ruthless self-interest than the French; the Frogs agree with the Finns. No countries are more determined to move from poverty to progress than the Indians and the Chinese. They have both invested heavily in nuclear power.

That is the big environmental question which Messrs Brown and Cameron will have to debate. By comparison, everything else is a mere skirmish. At some stage, a British politician will have to be prepared to expend political capital in the cause of converting the public to nuclear power.